The knee of the angel at left shows Lucas van Leyden’s important contribution to the development of tone in engraving technique. He achieved the effect of modeled shadow by cutting courses of curved parallel lines and then adding shorter lines in between. In comparison, Lucas’s contemporary Albrecht Dürer rarely applied this formula for shading, instead preferring a system of straight, crossed lines with flicking. Lucas’s technique may have influenced the invention of the engraved swelling groove some forty years later, which would achieve the same general effect with fewer lines.